Cards are a common organizing unit for modern user interfaces (UI). At their core, they’re just rectangular containers with borders and padding. However, when utilized properly to group related information, they help users better digest, engage, and navigate through content. This is why most successful dashboard/UI frameworks make cards a core feature of their component library. This article provides an overview of the API that bslib provides to create Bootstrap cards.
Setup code
To demonstrate that bslib cards work outside of Shiny (i.e., in R Markdown, static HTML, etc), we’ll make repeated use of statically rendered htmlwidgets like plotly and leaflet. Here’s some code to create those widgets:
library(bslib)
library(shiny)
library(htmltools)
library(plotly)
library(leaflet)
plotly_widget <- plot_ly(x = diamonds$cut) %>%
config(displayModeBar = FALSE) %>%
layout(margin = list(t = 0, b = 0, l = 0, r = 0))
leaflet_widget <- leafletOptions(attributionControl = FALSE) %>%
leaflet(options = .) %>%
addTiles()Shiny usage
Cards work equally well in Shiny. In the examples below, replace plotly_widget with plotlyOutput() and leaflet_widget with leafletOutput() to adapt them for Shiny server-rendered plots/maps.
Hello card()
A card() is designed to handle any number of “known” card items (e.g., card_header(), card_body(), etc) as unnamed arguments (i.e., children). As we’ll see shortly, card() also has some useful named arguments (e.g., full_screen, height, etc).
At their core, card() and card items are just an HTML div() with a special Bootstrap class, so you can use Bootstrap’s utility classes to customize things like colors, text, borders, etc.
card(
card_header(
class = "bg-dark",
"A header"
),
card_body(
markdown("Some text with a [link](https://github.com)")
)
)Some text with a link
Implicit card_body()
If you find yourself using card_body() without changing any of its defaults, consider dropping it altogether since any direct children of card() that aren’t “known” card() items, are wrapped together into an implicit card_body() call.1 For example, the code to the right generates HTML that is identical to the previous example:
card(
card_header(
class = "bg-dark",
"A header"
),
markdown("Some text with a [link](https://github.com).")
)Some text with a link.
Restricting growth
By default, a card()’s size grows to accommodate the size of it’s contents. Thus, if a card_body() contains a large amount of text, tables, etc., you may want to specify a height or max_height. That said, when laying out multiple cards, it’s likely best not to specify height on the card(), and instead, let the layout determine the height layout_column_wrap().
Although scrolling is convenient for reducing the amount of space required to park lots of content, it can also be a nuisance to the user. To help reduce the need for scrolling, consider pairing scrolling with full_screen = TRUE (which adds an icon to expand the card’s size to the browser window). Notice how, when the card is expanded to full-screen, max_height/height won’t effect the full-screen size of the card.
card(
max_height = 250,
full_screen = TRUE,
card_header(
"A long, scrolling, description"
),
lorem::ipsum(paragraphs = 3, sentences = 5)
)Dolor iaculis risus bibendum sollicitudin himenaeos facilisis ornare sed! Interdum proin, dapibus, laoreet est mi convallis tellus mollis. Euismod lectus mollis porttitor leo tempus primis parturient cras nunc. At dui; platea ultrices imperdiet magna mollis mauris commodo. Libero eleifend justo massa magna gravida nisi, ullamcorper pretium in faucibus conubia platea, metus nunc, eleifend quam facilisis curabitur nascetur, suscipit imperdiet ornare.
Sit mauris ornare fringilla placerat condimentum aliquet rutrum sed cubilia laoreet parturient. Ac condimentum integer sollicitudin vitae habitant magnis porta feugiat. Non at metus vivamus: natoque elementum facilisi senectus? Molestie lobortis dis felis, nisl tortor pretium himenaeos auctor laoreet, primis nullam lectus. Mauris nibh accumsan?
Sit sapien porta himenaeos sagittis eleifend facilisis sollicitudin tincidunt? Velit senectus feugiat aenean vulputate ac leo quisque lectus nascetur. Orci primis himenaeos, lectus nullam viverra purus! Quis sociis congue non sem malesuada erat, cras etiam molestie? Bibendum montes ridiculus sagittis aptent elementum venenatis – dignissim fringilla nec auctor montes in magna eleifend dapibus laoreet sociosqu cras mauris massa pellentesque ridiculus duis!
Filling outputs
A card()’s default behavior is optimized for facilitating filling layouts. More specifically, if a fill item (e.g., plotly_widget), appears as a direct child of a card_body(), it resizes to fit the card()s specified height. This means, by specifying height = 250 we’ve effectively shrunk the plot’s height from its default of 400 down to about 200 pixels. And, when expanded to full_screen, the plot grows to match the card()’s new size.
card(
height = 250,
full_screen = TRUE,
card_header("A filling plot"),
card_body(plotly_widget)
)Most htmlwidgets (e.g., plotly, leaflet, etc) and some other Shiny output bindings (e.g, plotOutput(), imageOutput(), etc) are fill items by default, so this behavior “just works” in those scenarios. And, in some of these situations, it’s helpful to remove card_body()’s padding, which can be done via spacing & alignment utility classes.
card(
height = 275,
full_screen = TRUE,
card_header("A filling map"),
card_body(
class = "p-0",
leaflet_widget
),
card_footer(
class = "fs-6",
"Copyright 2023 RStudio, PBC"
)
)Fill item(s) aren’t limited in how much they grow and shrink, which can be problematic when a card becomes very small. To work around this, consider adding a min_height on the card_body() container. For example, try using the handle on the lower-right portion of this card example to make the card taller/smaller.
This interactive example is a bit contrived in that we’re using CSS resize to demonstrate how to make plots that don’t shrink beyond a certain point, but this concept becomes quite useful when implementing page-level filling layouts (i.e., page_fillable()) with multiple cards.
card(
height = 300,
style = "resize:vertical;",
card_header("Plots that grow but don't shrink"),
card_body(
min_height = 250,
plotly_widget,
plotly_widget
)
)Troubleshooting fill
As you’ll learn more about in filling layouts, a fill item loses its ability to fill when wrapped in additional UI element that isn’t a fillable container. To fix the situation, use as_fill_carrier() to allow the additional element to carry the potential to fill from the card_body() down to the fill item.
Multiple card_body()
A card() can have multiple card_body()s, which is especially useful for:
- Combining both resizable and non-resizable contents (i.e., fill items and non-fill).
- Allowing each
card_body()to have their own styling (via inline styles and/or utility classes) and resizing limits (e.g.,min_height).
For example, when pairing filling output with scrolling content, you may want min_height on the filling output since the scrolling content will force it to shrink:
card(
height = 375,
full_screen = TRUE,
card_header(
"Filling plot, scrolling description"
),
card_body(
min_height = 200,
plotly_widget
),
card_body(
class = "lead container",
lorem::ipsum(paragraphs = 10, sentences = 5)
)
)Consectetur platea taciti cras auctor. Laoreet fames imperdiet magna, turpis scelerisque non malesuada pharetra pretium dis dui. Senectus commodo sapien, est quis duis pretium laoreet mi? Quam hac felis hendrerit, est lectus leo eros porta. Nibh sollicitudin dui enim mollis curae enim – sapien fermentum ultricies enim sagittis natoque malesuada platea.
Adipiscing tincidunt lacus bibendum fusce rutrum, sem mattis inceptos! Placerat nisl natoque dictum velit pellentesque ante nisi: pulvinar sem praesent! Laoreet enim nisi, lobortis ultricies purus suscipit ultrices quis. Dignissim dapibus platea mus rutrum dapibus senectus magnis class inceptos platea? Taciti torquent molestie vulputate?
Consectetur feugiat consequat, volutpat rutrum duis in diam phasellus. In sagittis lacinia sapien eleifend, vivamus per, eros mus platea nulla malesuada dignissim fames! Felis cubilia vel, phasellus auctor ultrices, quis ac pulvinar sociis massa. Tellus semper risus, sapien donec donec libero faucibus interdum. Libero vel luctus magna augue feugiat purus per.
Elit risus vestibulum inceptos ad: suscipit penatibus fringilla non aenean mus euismod quisque orci? Primis mus sapien sagittis vitae taciti vulputate placerat penatibus. At facilisi per tellus vivamus sem libero bibendum? Non velit platea tempus libero, platea magnis sollicitudin per? Consequat commodo cum tristique augue cubilia urna inceptos etiam vestibulum fringilla elementum mi sapien.
Consectetur dui blandit porttitor ultricies bibendum at sodales vel scelerisque blandit. Vel nulla vestibulum nam tempor aenean pretium blandit? Tempus aptent mollis pellentesque litora dis fringilla feugiat dictumst. Magnis praesent – nostra proin viverra consequat eros tristique tortor duis? Facilisis ridiculus ut tempus quis posuere duis vehicula odio – vulputate aenean eleifend volutpat, in: viverra: rhoncus habitant himenaeos quam auctor.
Dolor dignissim augue id scelerisque, nascetur, habitasse urna dignissim phasellus ullamcorper ad? Mattis vivamus felis morbi potenti id pretium neque ridiculus condimentum id. Suspendisse molestie vel massa condimentum, cubilia tortor conubia ante orci penatibus ac suspendisse? Justo congue tincidunt sodales purus iaculis risus sollicitudin diam sociis aliquam ullamcorper. Magna sem purus eros feugiat facilisi, eleifend, orci tempus quisque laoreet porta!
Amet ultricies risus; vestibulum nunc penatibus lacinia tincidunt, torquent tempor urna justo! Tortor condimentum elementum ligula libero aliquam non auctor tincidunt posuere semper velit. Libero ullamcorper eros volutpat dapibus velit lacinia – per dui aliquam sociosqu pellentesque aliquam egestas magna! Euismod est hac purus, suspendisse, nibh montes cras venenatis. Pretium ante pulvinar non?
Dolor senectus sollicitudin consequat nisl etiam dictum sed posuere laoreet mus hendrerit nascetur lacinia. Interdum mattis vivamus a per nibh odio orci mauris? Taciti egestas ultricies erat, quis ultricies lectus duis sem vulputate morbi! Justo accumsan taciti molestie mollis habitasse habitant! Na habitant.
Dolor gravida cum sagittis – est primis convallis at mus duis nulla? Platea habitasse libero nullam cras ad sociosqu – eros tortor est pulvinar at. Et velit quam massa ad bibendum ante accumsan montes curabitur. Himenaeos lobortis convallis dapibus suscipit aliquam imperdiet urna pulvinar. Nisi nam nullam massa duis hendrerit purus lobortis donec dis accumsan enim eros neque sagittis ac.
Ipsum mollis pellentesque: cursus bibendum eros: vitae imperdiet. Dis nascetur ultrices sociosqu donec dapibus ad suspendisse lacinia? Facilisi libero, pulvinar nam metus parturient: bibendum mattis ante? Nam dui quis donec ante congue commodo orci? Aliquet rhoncus platea scelerisque conubia hac velit dui penatibus at.
Also, when the content has a fixed size, and should not be allowed to scroll, set fill = FALSE:
card(
height = 350,
full_screen = TRUE,
card_header(
"Filling plot, short description"
),
plotly_widget,
card_body(
fill = FALSE,
card_title("A subtitle"),
p(class = "text-muted", "And a caption")
)
)A subtitle
And a caption
Multiple columns
As you’ll learn in column-based layouts, layout_column_wrap() is great for multi-column layouts that are responsive and accommodate for filling output. Here we have an equal-width 2-column layout using width = 1/2, but it’s also possible to have varying column widths.
card(
height = 350,
full_screen = TRUE,
card_header("A multi-column filling layout"),
card_body(
min_height = 200,
layout_column_wrap(
width = 1/2,
plotOutput("p1"),
plotOutput("p2")
)
),
lorem::ipsum(paragraphs = 3, sentences = 5)
)Sit interdum habitasse; cursus sed aptent in leo. Morbi tincidunt ante donec aptent gravida, dui lacinia, eget fusce ridiculus proin. Magnis velit, posuere eros nec, purus vel massa – lacinia bibendum sem. Neque sagittis mauris quisque lectus iaculis senectus, hendrerit leo. Purus aliquam aptent mollis enim.
Amet volutpat, senectus duis ac – vehicula laoreet dignissim fermentum elementum sagittis class quis? Magnis fringilla ligula posuere bibendum. Commodo vehicula tortor quam pellentesque quam mattis fusce? Natoque eros sociis, vehicula bibendum convallis mattis aliquam placerat. Primis aliquam iaculis morbi sociosqu hendrerit gravida, dictumst iaculis, facilisi condimentum volutpat, mi condimentum lectus.
Elit ut aptent, sociis, quis nibh fames tempor litora diam. Turpis dictum varius ornare nascetur duis posuere hac integer vulputate condimentum curabitur? Nunc dictum non montes tortor montes commodo urna hac iaculis risus lectus. Sollicitudin lacus vestibulum ad aptent sed odio, ullamcorper est fusce at vulputate? Na vulputate.
Multiple cards
layout_column_wrap() is especially nice for laying out multiple cards since each card in a particular row will have the same height (by default). Learn more in column-based layouts.
layout_column_wrap(
width = 1/2,
height = 300,
card(full_screen = TRUE, card_header("A filling plot"), plotly_widget),
card(full_screen = TRUE, card_header("A filling map"), card_body(class = "p-0", leaflet_widget))
)Multiple tabs
navs_tab_card() and navs_pill_card() make it possible to create cards with multiple tabs or pills. These functions have the same full_screen capabilities as normal card()s as well some other options like title (since there is no natural place for a card_header() to be used). Note that, each nav() object is similar to a card(). That is, if the direct children aren’t already card items (e.g., card_title()), they get implicitly wrapped in a card_body().
library(leaflet)
navs_tab_card(
height = 450,
full_screen = TRUE,
title = "HTML Widgets",
nav(
"Plotly",
card_title("A plotly plot"),
plotly_widget
),
nav(
"Leaflet",
card_title("A leaflet plot"),
leaflet_widget
),
nav(
shiny::icon("circle-info"),
markdown("Learn more about [htmlwidgets](http://www.htmlwidgets.org/)")
)
)Sidebars
As you’ll learn more about in sidebar layouts, layout_sidebar() just works when placed inside in a card(). In this case, if you want fill items (e.g., plotly_widget) to still fill the card like we’ve seen before, you’ll need to set fillable = TRUE in layout_sidebar().
card(
height = 300,
full_screen = TRUE,
card_header("A sidebar layout inside a card"),
layout_sidebar(
fillable = TRUE,
sidebar(
actionButton("btn", "A button")
),
plotly_widget
)
)Static images
card_image() makes it easy to embed static (i.e., pre-generated) images into a card. Provide a URL to href to make it clickable. In the case of multiple card_image()s, consider laying them out in multiple cards with layout_column_wrap() to produce a grid of clickable thumbnails.
card(
height = 300,
full_screen = TRUE,
card_image(
file = "shiny-hex.svg",
href = "https://github.com/rstudio/shiny"
),
card_body(
fill = FALSE,
card_title("Shiny for R"),
p(
class = "fw-light text-muted",
"Brought to you by RStudio."
)
)
)Flexbox
Both card() and card_body() default to fillable = TRUE (that is, they are CSS flexbox containers), which works wonders for facilitating filling outputs, but it also leads to surprising behavior with inline tags (e.g., actionButton(), span(), strings, etc). Specifically, each inline tag is placed on a new line, but in a “normal” layout flow (fillable = FALSE), inline tags render inline.
card(
card_body(
fillable = TRUE,
"Here's some", tags$i("inline"), "text",
actionButton("btn1", "A button")
),
card_body(
fillable = FALSE,
"Here's some", tags$i("inline"), "text",
actionButton("btn2", "A button")
)
)That said, sometimes working in a flexbox layout is quite useful, even when working with inline tags. Here we leverage flexbox’s gap property to control the spacing between a plot, a (full-width) button, and paragraph. Note that, by using markdown() for the paragraph, it wraps the results in a <p> tag, which means the contents of the paragraph are not longer subject to flexbox layout. If we wanted, we could do something similar to render the actionButton() inline by wrapping it in a div().
card(
height = 325, full_screen = TRUE,
card_header("A plot with an action links"),
card_body(
class = "gap-2 container",
plotly_widget,
actionButton(
"go_btn", "Action button",
class = "btn-primary rounded-0"
),
markdown("Here's a _simple_ [hyperlink](https://www.google.com/).")
)
)Here's a simple hyperlink.
In addition to gap, flexbox has really nice ways of handling otherwise difficult spacing and alignment issues. And, thanks to Bootstrap’s flex utility classes, we can easily opt-in and customize defaults.
card(
height = 300, full_screen = TRUE,
card_header(
class = "d-flex justify-content-between",
"Centered plot",
checkboxInput("check", " Check me", TRUE)
),
card_body(
class = "align-items-center",
plotOutput("id", width = "75%")
)
)Shiny
Since this article is statically rendered, the examples here use statically rendered content/widgets, but the same card() functionality works for dynamically rendered content via Shiny (e.g., plotOutput(), plotlyOutput(), etc).
An additional benefit that comes with using shiny is the ability to use getCurrentOutputInfo() to render new/different content when the output container becomes large enough, which is particularly useful with card(full_screen = T, ...). For example, you may want additional captions/labels when a plot is large, additional controls on a table, etc (see the value boxes article for a clever use of this).
# UI logic
ui <- page_fluid(
card(
max_height = 200,
full_screen = TRUE,
card_header("A dynamically rendered plot"),
plotOutput("plot_id")
)
)
# Server logic
server <- function(input, output, session) {
output$plot_id <- renderPlot({
info <- getCurrentOutputInfo()
if (info$height() > 600) {
# code for "large" plot
} else {
# code for "small" plot
}
})
}
shinyApp(ui, server)Appendix
The following CSS is used to give plotOutput() a background color; it’s necessary here because this documentation page is not actually hooked up to a Shiny app, so we can’t show a real plot.